Health monitoring of components is used in predictive maintenance to assist with determining when maintenance should be performed. This provides significant cost-savings over scheduled routine maintenance which is typically based on worst case scenarios. Typically a value of ‘remaining useful life’, or RUL, is output as a time interval to the next appropriate maintenance requirement.
In aircraft fuel systems fuel pumps are used to feed fuel to the engines, so-called ‘engine feed pumps’, and to transfer fuel between fuel tanks, so-called ‘transfer pumps’. Both these fuel pumps are typically electrically driven and operate as either single speed direct current (DC) or variable speed variable current devices.
Several methods utilising model-based conditioning (health) monitoring for pumps are known, e.g. U.S. Pat. No. 6,709,240, U.S. Pat. No. 6,757,665 and US 2004/0230384. These model-based health monitoring techniques generally involve analysis of the pump motor's current or electrical signature, or by detecting low flow or cavitation in the pump, and compares these to one or more models of the pump's characteristics obtained from laboratory testing. Differences between the real-world and laboratory characteristic signals can be computed to infer health status or failure mode of the motor and/or pump. The health monitoring may be performed continuously or at intervals.
A major drawback of existing model-based health monitoring techniques is that the pump may not perform in the real-world as expected from laboratory testing, making the current model-based health monitoring techniques inaccurate. This can lead to higher performance margins being applied and earlier maintenance being predicted that what is actually required which is costly, particularly in the aviation industry where the fuel pump is not only a critical part but is also difficult to access often necessitating taking the aircraft out of service to maintain, replace or repair.